X-ray imaging of the human breast to detect malignancies has been clinically available since about 1970. As might very well be expected, since then, over the period of almost half a century the technology has undergone a number of changes and refinements. Initially, X-ray images were captured on film. Today X-ray breast images are directly captured by arrays of small X-ray detectors which convert intensity of X-rays incident on the detectors to electrical signals. The electrical signals are digitized to provide digital representations of the images that are stored in computers for later diagnoses.
A relatively recent change in X-ray breast imaging technology that was made practical by digital X-ray imaging is referred to as spectral contrast enhanced digital mammography (SCEDM). In SCEDM a patient is injected with a contrast agent that is preferably taken up by cancerous lesions in the patient's breast. The breast is exposed to X-rays at two different energies, typically a relatively low X-ray energy at which the contrast agent is a relatively poor absorber of X-rays and a relatively high X-ray energy at which the contrast agent is a relatively good absorber of X-rays. The exposures to the high and low energy X-rays provide high and low energy X-ray digital images respectively of the breast. The images are digitally subtracted to provide a “subtracted image” in which concentrations of the contrast agent in the breast, and thereby malignant lesions in the breast, generally have enhanced contrast and visibility. In particular, for dense breast tissues, known to be relatively opaque in classical mammography, normal breast tissue becomes substantially transparent in the subtracted image, enhancing contrast of lesions that in conventional non-subtracted X-ray images may be difficult to discern. Typically, the contrast agent used to acquire the high and low X-ray images is an iodine based contrast agent, and the low energy X-rays have an energy below the k-edge of iodine and the high energy X-rays have an energy above the k-edge of iodine.
Although SCEDM has the potential to improve sensitivity of mammography, in practice, a relatively large number of biopsies is performed on lesions detected in SCEDM images that turn out to be benign. More than 60% of the biopsies triggered by a lesion detected in SCEDM are actually performed on benign lesions. The relatively large number of biopsies that turn out to be unnecessary imposes a relatively high financial cost and psychological burden on patients and society.